Severe Thunderstorm Warning 11, NWS Grand Junction, CO

Area Forecast Discussion
National Weather Service Grand Junction CO
352 AM MDT Tue Aug 21 2018

.SHORT TERM...(Today through Wednesday)
Issued at 351 AM MDT Tue Aug 21 2018

One sure fire way to know if the monsoon has kicked in is
nighttime convection. Guess what we've been seeing all
night...plenty of showers and storms across the area. Areas along
and north of I-70 are the winners though some showers and storms
are moving near Nucla and the San Juans at this hour. This
convection is in response to a shortwave and the increasing
moisture available. Forecast thinking remains the same for today.
PWATs will continue to increase as high pressure is in a favorable
location to advect moisture from the south. To our northwest, an
elongated trough/area of low pressure will keep that high pressure
in place. This afternoon and evening, a disturbance will move up
from the south and cause widespread showers and thunderstorms.
Cloud cover will likely remain in place today which will inhibit
convection to a degree. Even so, dynamics aloft should overcome
some of the cloud cover allowing embedded storms to fire. The
NAM12 and GFS are in fairly good agreement with the heavier
precipitation to start later this afternoon and evening. The
NAMNEST also showing some heavier precipitation but not as
widespread or lasting as long. Looks like areas along and north of
I-70 will see the heavier rain and this makes sense as the jet
stream is positioned more to our north allowing more lift in that
particular area. Having said that, a secondary wave is progged to
move over our southern areas Tuesday night through Wednesday
morning so don't worry Cortez, Durango, Pagosa Springs and areas
in between. You'll get yours, just a bit later.

Wednesday looks very similar to Tuesday. The high to our
southeast will remain fairly stationary while the trough to the
northwest moves eastward. In fact, the trough looks to move
through late Wednesday night into early Thursday morning, and it
will be the focus of precipitation. Another day of widespread
convection is anticipated.

Smoke should be outta here thanks to mixing and the
precipitation. Temperatures will also drop thanks to cloud cover
and rainfall and will be a welcome respite after the many days of
above 90+ degree temperatures.

.LONG TERM...(Wednesday night through Monday)
Issued at 351 AM MDT Tue Aug 21 2018

Shower and thunderstorm activity looks to continue through the
overnight hours into Thursday morning as the low over the Pacific
Northwest opens up and tracks across the northern Rockies states
of Idaho, Montana and Wyoming. This low will drag yet another
shortwave disturbance through the area. Conditions dry out
significantly behind this passing shortwave trough by Thursday as
the flow shifts around to westerly and precipitable water (PW)
values drop below 0.5 inches across much of the area with a
shortwave ridge sliding over the area from the west. Some higher
PW above 0.75 inches look to remain near the Four Corners and
thinking that enough moisture will be in place for afternoon
thunderstorm development over the higher terrain along the divide.
Coverage will drop though and be isolated to scattered at best
with activity dying down near sunset as no shortwaves look to
sustain convection. Friday also appears to be a mostly dry day but
a little more storm activity may be seen over the high terrain as
we transition back to southwest flow by the weekend.

The area of high pressure to our southeast restrengthens by the
weekend into next week as a trough of low pressure reloads over
the Pacific Northwest. This allows for southwest flow to set up
once again, which is the favorable monsoon pattern we have been
long waiting for...just a little late to the game. PW values climb
back to 0.75 and above with pockets of inch plus values here and
there. The pattern seems good though for daily afternoon
thunderstorm activity over all mountains with some drift into
valleys late afternoon and evening through much of next week
looking ahead at long term model guidance. It is uncertain how
much of this convection would linger during overnight hours as
this is all predicated from fine mesoscale details and embedded
shortwaves that are difficult to resolve this far out.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 351 AM MDT Tue Aug 21 2018

Light rain showers and a few thunderstorms will continue this
morning, generally for the northern valleys and the San Juans.
This showery activity will become more isolated through the
morning hours. After 18Z, convection will begin again bringing
widespread rain and some embedded convection to the region.
Chances for VCTS or -TSRA looks possible for almost all TAF sites.
Ceilings should remain VFR for the most part though a quick, brief
drop to MVFR not out of the question. Do anticipate MVFR for
visibility under the heavier showers and storms. IFR breakpoints
will likely be met for KASE, KEGE, and KRIL today though other
airports may also meet them as convection gets going. Conditions
not expected to improve through the next 24 hours.

&&

.HYDROLOGY...
Issued at 351 AM MDT Tue Aug 21 2018

Heavier rainfall from showers and storms today may cause some
issues for burn scars across the region. Even minor amounts of
rain over these scars can and have caused flash flooding, debris
flows, and mud slides. With that in mind, issued a flash flood
watch mainly for those areas. While the graphic on weather.gov/gjt
will show large areas under the watch, they are really only for
the burn scars. The following fires are where we're concerned
about for the flash flood watch: 416, Burro, West Guard, Bull
Draw, Lake Christine, Cache Creek, Red Canyon, Cabin Lake, Indian
Valley, and Divide.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Flash Flood Watch from noon MDT today through Wednesday morning
     for COZ001>003-008>010-013-017-019-021-022.

UT...None.
&&

SHORT TERM...TGR
LONG TERM...MDA
AVIATION...TGR
HYDROLOGY...TGR

Hazardous Weather Outlook
National Weather Service Grand Junction CO
547 AM MDT Tue Aug 21 2018

COZ001>014-017>023-UTZ022>025-027>029-221200-
Lower Yampa River Basin-Central Yampa River Basin-
Roan and Tavaputs Plateaus-Elkhead and Park Mountains-
Upper Yampa River Basin-Grand Valley-Debeque to Silt Corridor-
Central Colorado River Basin-Grand and Battlement Mesas-
Gore and Elk Mountains/Central Mountain Valleys-
Central Gunnison and Uncompahgre River Basin-
West Elk and Sawatch Mountains-Flat Tops-
Upper Gunnison River Valley-Uncompahgre Plateau and Dallas Divide-
Northwest San Juan Mountains-Southwest San Juan Mountains-
Paradox Valley/Lower Dolores River-
Four Corners/Upper Dolores River-Animas River Basin-
San Juan River Basin-Southeast Utah-Eastern Uinta Mountains-
Eastern Uinta Basin-Tavaputs Plateau-Arches/Grand Flat-
La Sal and Abajo Mountains-Canyonlands/Natural Bridges-
547 AM MDT Tue Aug 21 2018

This hazardous weather outlook is for eastern Utah and western
Colorado.

.DAY ONE...Today and Tonight

Showers and thunderstorms will be common across the entire
forecast area today as monsoonal moisture has returned. Some of
the convection will be heavy. A flash flood watch has been issued
for the burn scars across the area as low amounts of rainfall can
create flash flooding, mud slides, and debris flows. Rainfall will
continue overnight.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Shower and storms will continue into Wednesday bringing more
precipitation to the area. Drying conditions will kick in Thursday
and Friday before another round of showers and storms moves in for
the weekend.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

Special Weather Statement
National Weather Service Grand Junction CO
1050 AM MDT TUE AUG 21 2018

COZ006-017-211715-
Uncompahgre Plateau/Dallas Divide CO-Grand Valley CO-
1050 AM MDT TUE AUG 21 2018

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN MESA COUNTY UNTIL 1115 AM
MDT...

At 1050 AM MDT, Doppler radar was tracking a strong thunderstorm 12
miles southwest of Grand Junction, moving northeast at 25 mph. This
storm was located near Glade Park.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Grand Junction, Orchard Mesa, Glade Park, Redlands, Fruitvale and
Clifton.

This includes the following highways...
 Interstate 70 in Colorado near mile marker 30.
 U.S. Highway 50 in Colorado between mile markers 32 and 38.

LAT...LON 3894 10876 3899 10879 3912 10856 3908 10849
      3900 10848
TIME...MOT...LOC 1650Z 243DEG 22KT 3898 10873

Charnick

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Special Weather Statement
National Weather Service Grand Junction CO
1108 AM MDT TUE AUG 21 2018

COZ003-006-007-211800-
Roan and Tavaputs Plateaus CO-Debeque to Silt Corridor CO-
Grand Valley CO-
1108 AM MDT TUE AUG 21 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL MESA COUNTY UNTIL
NOON MDT...

At 1108 AM MDT, Doppler radar was tracking a strong thunderstorm
near and just north of Grand Junction, moving northeast at 30 mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Grand Junction.

LAT...LON 3912 10859 3915 10862 3937 10840 3933 10831
      3925 10827
TIME...MOT...LOC 1708Z 229DEG 28KT 3915 10858

Charnick

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1113 AM MDT TUE AUG 21 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1023 AM     TSTM WND GST     PINTO, MASSADONA 18SE   40.02N 108.40W
08/21/2018  M45 MPH          RIO BLANCO         CO   MESONET

            MESONET STATION PIRC2, PINTO, MASSADONA
            18SE.

&&

NL